(1) Field of the Invention
This invention relates to a roll-over suppressing control apparatus for a vehicle wherein the braking force is controlled in response to a rolling state of the vehicle upon turning to suppress the roll-over of the vehicle.
(2) Description of the Related Art
Upon general turning or upon special turning such as upon lane change of a vehicle, depending upon the traveling speed or the steering situation of the vehicle, a moment in the rolling direction is generated on the vehicle, and there is the possibility that the moment may cause roll-over (turning over on its side) of the vehicle. Therefore, various apparatus have been proposed conventionally including an apparatus which issues, if the possibility of roll-over occurs with a vehicle, a notification of the possibility to the driver and an apparatus which takes a countermeasure for the safety, a braking countermeasure or a like countermeasure before a vehicle is brought into roll-over thereby to prevent the possible roll-over.
For example, as a technique for suppressing roll-over of a vehicle, a technique has been developed wherein the rolling angle of a vehicle is detected to determine the risk of the rolling state of the vehicle and a warning is issued to the driver at an early stage and braking control is performed in response to the risk (refer to Japanese Patent Laid-Open No. 2002-168620). According to the technique described, the rolling angle θ of the vehicle is arithmetically operated based on a signal of a vehicle height sensor, and the roll rate (rolling angular velocity) ω is arithmetically operated based on the rate of change of the rolling angle θ. Then, a roll emergency as a scale indicating the magnitude of the risk of roll-over of the vehicle is decided based on the magnitude of the roll rate ω. Then, it is decided based on the roll emergency and the rolling angle θ whether or not there is the risk that the vehicle may roll over, and slowdown control is executed and a warning lamp and a warning device are rendered operative to give a warning to the driver based on a result of the decision of the risk of the roll-over.
As a similar technique, also a technique wherein an air brake system is rendered operative in response to the magnitude of the roll rate (rolling angular velocity) of a vehicle has been proposed (refer to, for example, Japanese Patent Laid-Open No. Hei 11-11272). According to the technique described, the roll rate generated on the vehicle body is detected by a rate sensor, and a target deceleration is set among three stages based on the state of the roll rate and the level of the steering angular velocity. Then, the air brake system is operated in accordance with the target deceleration to slow down the vehicle thereby to suppress otherwise possible roll-over of the vehicle.
However, where roll-over suppressing control is performed in response to the roll rate of a vehicle as described above, if a roll-over suppressing control amount is set simply in accordance with the value of the roll rate, then suppression of roll-over cannot necessarily be performed appropriately.
For example, in the case of general one-directional turning, since the roll rate gradually increases, even if the roll-over suppressing control amount is set to a comparatively low value with respect to the roll rate, the roll-over can be suppressed sufficiently. However, in the case of steering back turning wherein the turning direction changes over halfway as represented by lane change, the roll rate increases rapidly, which is likely to cause roll-over of the vehicle, and therefore, if the roll-over suppressing control amount is not set to a high value relative to the roll rate, there is the possibility that the roll-over may not be suppressed with certainty.
Further, if the roll-over suppressing control amount is set to a high value relative to the roll rate in order to solve such a subject as just described, then although roll-over upon steering back turning such as upon lane change can be suppressed effectively by the great control amount, upon general one-directional turning, excessively high braking force which is not commensurate with the risk of the roll-over acts and slows down the vehicle suddenly, resulting in deterioration of the traveling performance of the vehicle and also in hurt of the feeling of the driver.
In short, even if the detection value of the roll rate is equal, the risk of roll-over differs depending upon the turning situation (type of turning) of the vehicle, and the braking control amount for suppressing roll-over of the vehicle should be determined not only setting it so as to correspond to a parameter indicative of a rolling state such as the roll rate but also taking the type of turning into consideration such as whether the turning is general one-directional turning or steering back turning (for example, upon lane change or upon S-shaped curve traveling).